Method for enhancing crystallinity of polycarbonates

Abstract

The crystallinity of an amorphous precursor polycarbonate is enhanced by contact in the liquid or vapor state with a non-solvent which may be water, an alkanol or a mixture thereof and which is dialkyl carbonate-free. Contact temperatures are at least about 75° C. and are further defined by the relationship T.sub.c ≧T.sub.b -z, wherein T c is the contact temperature, T b is the boiling point of the non-solvent at the contact pressure employed (both in degrees C.) and z is a constant whose value is 60.

What is claimed is: 
     
       1. A method for enhancing the crystallinity of a solid, amorphous aromatic precursor polycarbonate which comprises contacting said precursor polycarbonate with at least one non-solvent therefor, said non-solvent being water or a C 1-20  alkanol in the liquid or vapor state and being free from dialkyl carbonate, for a time effective to form a surface-crystallized polycarbonate and at a contact temperature and pressure, said contact temperature being at least about 75° C. and being further defined by the relationship   T.sub.c ≧T.sub.b -z,     wherein T c  is the contact temperature, T b  is the boiling point of the non-solvent at the contact pressure employed (both in degrees C.) and z is a constant whose value is 60.   
     
     
       2. A method according to claim 1 wherein the precursor polycarbonate is a homopolycarbonate. 
     
     
       3. A method according to claim 1 wherein the precursor polycarbonate is a copolycarbonate. 
     
     
       4. A method according to claim 3 wherein the precursor polycarbonate is a copolyestercarbonate. 
     
     
       5. A method according to claim 1 wherein the precursor polycarbonate is a bisphenol A homo- or copolycarbonate. 
     
     
       6. A method according to claim 1 wherein the precursor polycarbonate is an oligomer having a weight average molecular weight in the range of about 2,000-10,000 as determined by gel permeation chromatography. 
     
     
       7. A method according to claim 1 wherein the precursor polycarbonate has a weight average molecular weight in the range of about 10,000-35,000 as determined by gel permeation chromatography. 
     
     
       8. A method according to claim 1 wherein the precursor polycarbonate is a branched polycarbonate. 
     
     
       9. A method according to claim 1 wherein the precursor polycarbonate is a recycled polycarbonate. 
     
     
       10. A method according to claim 1 wherein the non-solvent is water. 
     
     
       11. A method according to claim 1 wherein the non-solvent is a C 1-5  primary alkanol. 
     
     
       12. A method according to claim 1 wherein the non-solvent is methanol. 
     
     
       13. A method according to claim 12 wherein the precursor polycarbonate is an oligomer which is extruded into methanol and pelletized, thereby achieving simultaneous pelletization and crystallinity enhancement. 
     
     
       14. A method according to claim 1 wherein the non-solvent is water or a mixture of water and methanol. 
     
     
       15. A method for enhancing the crystallinity of a solid, amorphous aromatic precursor polycarbonate which comprises contacting said precursor polycarbonate with at least one non-solvent therefor, said non-solvent being water or a C 1-20  alkanol in the liquid or vapor state and being free from dialkyl carbonate, for a time effective to form a surface-crystallized polycarbonate and at a contact temperature and pressure, said contact temperature being at least about 75° C. and being further defined by the relationship   T.sub.c ≧T.sub.b -z,     wherein T c  is the contact temperature, T b  is the boiling point of the non-solvent at the contact pressure employed (both in degrees C.) and z is a constant whose value is 20.   
     
     
       16. A method according to claim 15 wherein the contact pressure is atmospheric pressure or an elevated pressure up to about 5 atm. 
     
     
       17. A method for preparing an aromatic polycarbonate which comprises: enhancing the crystallinity of a solid, amorphous aromatic precursor polycarbonate which comprises contacting said precursor polycarbonate with at least one non-solvent therefor, said non-solvent being water or a C 1-20  alkanol in the liquid or vapor state and being free from dialkyl carbonate, for a time effective to form a surface-crystallized polycarbonate and at a contact temperature and pressure, said contact temperature being at least about 75° C. and being further defined by the relationship   T.sub.c ≧T.sub.b -z,       wherein T c  is the contact temperature, T b  is the boiling point of the non-solvent at the contact pressure employed (both in degrees C.) and z is a constant whose value is 60; and   polymerizing the enhanced crystallinity precursor polycarbonate thus produced by solid state polymerization.   
     
     
       18. A method according to claim 17 wherein the precursor polycarbonate is a bisphenol A homo- or copolycarbonate. 
     
     
       19. A method according to claim 17 wherein the non-solvent is water. 
     
     
       20. A method according to claim 17 wherein the non-solvent is water, methanol or a mixture thereof.